WIP use $paths->systemDirectory in public/index.php

[samsonasik]

So it reduce manual change when changing system directory.

Checklist:

• Securely signed commits

[jim-parry]

This will work for now, but the solution will be different once we get the the simplified distributions in place.
I would like to defer this until then, and hopefully enlist your help making sure the distrubtions work as intended.

[samsonasik]

@jim-parry mergeable?

[jim-parry]

Yes. This makes one less file for my script to change :)